Hibernate参考指南：关系型持久化详解

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"Hibernate是Java语言中的一个对象关系映射（ORM）框架，其英文文档为 Hibernate Reference Documentation，版本为3.5.1-Final。该文档由Gavin King、Christian Bauer、Max Rydahl Andersen、Emmanuel Bernard和Steve Ebersole等人撰写，并感谢James Cobb和Cheyenne Weaver的图形设计工作。文档包含了对Hibernate的全面介绍，从基础教程到高级架构，旨在帮助开发者理解和使用Hibernate进行数据库操作。" 在Hibernate参考文档中，首先介绍了教程部分： 1. 教程（Tutorial）： - 第一部分是第一个Hibernate应用程序的建立。这一部分涵盖了基本环境的设置，包括如何创建第一个类，编写映射文件，配置Hibernate，以及如何使用Maven构建项目。此外，还讲解了启动和辅助类的使用，以及如何加载和存储对象。 - 第二部分涉及对象之间的关联映射。这里讲解了如何映射Person类，实现单向基于Set的关联，处理这些关联，以及集合值的映射。进一步，文档介绍了双向关联，包括如何工作和管理双向链接。 - 第三部分是EventManager web应用的构建。涵盖了基础Servlet的编写，处理和渲染数据的方法，以及应用的部署和测试步骤。 2. 架构（Architecture）： - 提供了Hibernate整体架构的概述，包括对象的状态（实例状态），如瞬时态、持久态和脱管态。 - 讨论了与Java管理扩展（JMX）的集成，使用户能够通过JMX监控和管理Hibernate服务。 - 描述了JCA（Java连接性架构）支持，使Hibernate可以作为EJB或应用服务器的一部分运行。 - 引入了上下文会话（Contextual sessions）的概念，它允许在特定上下文中（如Web请求）管理Hibernate会话，提供更好的事务管理和性能。这个文档不仅适合初学者了解Hibernate的基础用法，也对有经验的开发者深入理解Hibernate的内部机制提供了宝贵资料。通过学习和实践，开发者可以有效地将Java对象与关系数据库进行映射，简化数据库操作，提高开发效率。

Chapter 1. Tutorial

required. Hibernate can also access fields directly, the benefit of accessor methods is robustness

for refactoring.

The id property holds a unique identifier value for a particular event. All persistent entity classes

(there are less important dependent classes as well) will need such an identifier property if we want

to use the full feature set of Hibernate. In fact, most applications, especially web applications, need

to distinguish objects by identifier, so you should consider this a feature rather than a limitation.

However, we usually do not manipulate the identity of an object, hence the setter method should

be private. Only Hibernate will assign identifiers when an object is saved. Hibernate can access

public, private, and protected accessor methods, as well as public, private and protected fields

directly. The choice is up to you and you can match it to fit your application design.

The no-argument constructor is a requirement for all persistent classes; Hibernate has to create

objects for you, using Java Reflection. The constructor can be private, however package or public

visibility is required for runtime proxy generation and efficient data retrieval without bytecode

instrumentation.

Save this file to the src/main/java/org/hibernate/tutorial/domain directory.

1.1.3. The mapping file

Hibernate needs to know how to load and store objects of the persistent class. This is where

the Hibernate mapping file comes into play. The mapping file tells Hibernate what table in the

database it has to access, and what columns in that table it should use.

The basic structure of a mapping file looks like this:

<?xml version="1.0"?>

<!DOCTYPE hibernate-mapping PUBLIC

"-//Hibernate/Hibernate Mapping DTD 3.0//EN"

"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping package="org.hibernate.tutorial.domain">

[...]

</hibernate-mapping>

Hibernate DTD is sophisticated. You can use it for auto-completion of XML mapping elements

and attributes in your editor or IDE. Opening up the DTD file in your text editor is the easiest

way to get an overview of all elements and attributes, and to view the defaults, as well as some

comments. Hibernate will not load the DTD file from the web, but first look it up from the classpath

of the application. The DTD file is included in hibernate-core.jar (it is also included in the

hibernate3.jar, if using the distribution bundle).

Hibernate configuration

Tip

Hibernate makes this mapping type determination using reflection when the

mapping files are processed. This can take time and resources, so if startup

performance is important you should consider explicitly defining the type to use.

Save this mapping file as src/main/resources/org/hibernate/tutorial/domain/

Event.hbm.xml.

1.1.4. Hibernate configuration

At this point, you should have the persistent class and its mapping file in place. It is now time to

configure Hibernate. First let's set up HSQLDB to run in "server mode"

Note

We do this do that the data remains between runs.

We will utilize the Maven exec plugin to launch the HSQLDB server by running: mvn exec:java

-Dexec.mainClass="org.hsqldb.Server" -Dexec.args="-database.0 file:target/data/

tutorial" You will see it start up and bind to a TCP/IP socket; this is where our application will

connect later. If you want to start with a fresh database during this tutorial, shutdown HSQLDB,

delete all files in the target/data directory, and start HSQLDB again.

Hibernate will be connecting to the database on behalf of your application, so it needs to know

how to obtain connections. For this tutorial we will be using a standalone connection pool (as

opposed to a javax.sql.DataSource). Hibernate comes with support for two third-party open

source JDBC connection pools: c3p0 [https://sourceforge.net/projects/c3p0] and proxool [http://

proxool.sourceforge.net/]. However, we will be using the Hibernate built-in connection pool for

this tutorial.

Caution

The built-in Hibernate connection pool is in no way intended for production use. It

lacks several features found on any decent connection pool.

For Hibernate's configuration, we can use a simple hibernate.properties file, a more

sophisticated hibernate.cfg.xml file, or even complete programmatic setup. Most users prefer

the XML configuration file:

<?xml version='1.0' encoding='utf-8'?>

<!DOCTYPE hibernate-configuration PUBLIC

"-//Hibernate/Hibernate Configuration DTD 3.0//EN"

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